1. FIELD OF INVENTION
This invention relates to magnifying devices and, more particularly, to magnifying devices used in connection with measuring instruments.
2. BACKGROUND OF THE PRIOR ART
Measuring instruments used to perform scaling operations for architectural, engineering or mechanical drafting are well known. Such instruments have graduated spaces representing various scales marked along their length and are either of generally triangular cross section or of a relatively flat configuration.
In many situations, there is a need to magnify the graduated spaces marked on the measuring instrument. For example, magnification greatly reduces the likelihood that persons of normal vision will experience eye strain or fatigue as a result of prolonged detailed work. In addition, magnification assists visually impaired persons in making more accurate measurements. Further, magnification greatly facilitates the instruction of persons, such as students or beginning draftsmen, who are inexperienced in the proper use of such measuring instruments.
Currently, several methods are used to magnify measuring instruments and the adjacent work surface. The first and most obvious method is simply to transpose a hand-held magnifying glass between the eye of the draftsman and the measuring instrument. The primary disadvantage of this method is simply that a draftsman cannot, in one simultaneous and continuous operation, hold the magnifying glass, secure a measuring instrument in the desired location and manipulate a writing or marking tool. Because the draftsman must limit his simultaneous activities to those which can be accomplished properly with two hands, utilization of this method of magnification will inevitably result in decreased drafting efficiency.
A second method currently used to magnify measuring instruments is the utilization of an eye piece fitted with a magnifying lens. The primary problem with this method is that after each time such eye pieces are used, the draftsman must stop drawing in order to remove and store the eye piece. Because magnification is usually not required during every phase of drafting operations, this method is extremely inconvenient and results in decreased drafting efficiency. In addition, this type of eye piece limits the draftsman to the use of one eye, thereby introducing a potential source of measuring error and eye strain.
Another current method of magnifying measuring instruments is taught in U.S. Pat. No. 2,455,972. This method provides a magnifying lens concentrically secured to a pen, pencil or other writing or marking tool. The lens is shaped and secured to the tool so that the focal point of the lens will insure that the operator will see the magnified portion of the measuring instrument and tool in proper focus. This method of magnification has two distinct disadvantages. First, because the magnifying lens is secured to the writing tool, it is necessary for the draftsman to remove and re-install this device each time a change of writing tools is necessary. Because draftsmen frequently change pencils or pens, the use of this device is extremely inconvenient and results in lessened efficiency.
The second significant problem with the method of magnification taught in U.S. Pat. No. 2,455,972 is that the magnifying lens extends appreciably outside the circumference of the writing tool. As a result, this method is not suited for use in connection with measuring instruments of triangular configuration unless the vertical dimension of such instruments is substantially less than the distance from the working end of the writing tool to the lower surface of the lens. If this requirement is satisfied, the resulting device will have a configuration in which the user will be forced, because of the placement of the magnifying lens, to grasp the stem of the writing tool higher than is customary. As a result, this method has proven inefficient when used in connection with measuring instruments of triangular configuration.